From left, candidates John Fetterman, Katie McGinty, and Joe Sestak participate in a U.S. Democratic Primary Debate hosted by WPSU in University Park, Pennsylvania, on April 9.

When Braddock, Pennsylvania, Mayor John Fetterman announced his entrance into the state’s Democratic primary for U.S. Senate, there was a surge of enthusiasm from progressive activists. The biker-bearded Fetterman looked and sounded like an alternative to the candidates who had already announced—retired Admiral Joe Sestak and ex-state official Katie McGinty—both of whom look straight out of central casting for a senator from the Northeast, with the picture-perfect records to match.

Soon after Fetterman’s announcement, at a hip bar in an up-and-coming corner of Philadelphia, the candidate gave his stump speech—focused on inequality and poverty in the small former steel town he represents—to a small crowd of voters, many of whom were sporting Bernie Sanders paraphernalia and visible tattoos. (The mayor himself has prominent ink, with his town’s zip code on one arm and the dates of the nine murders that have occurred there since he took office on the other.) At the end of his speech, where he talked up universal pre-K, an animated young woman rocketed up from her seat and gave an impassioned plea for Fetterman.

“Half of good politics is just genuinely giving a shit,” Liz Arnold told the crowd. She’s an electrician by trade and a well-known local anti-fracking activist who is well versed in state politics and in commanding the attention of a room. “What other candidates do you know who have done this [lived in an impoverished town]? Sestak is who I’ve gotten behind in the past. But he says the wrong things and pisses off the wrong people. McGinty is the machine candidate. John doesn’t have any of that baggage.”

The small crowd cheered, and listeners rushed to sign up for Fetterman’s mailing list.

But now, six months later, with April 26 primary a week away, Fetterman trails badly in the polls. Few people have heard his message, and the latest poll on April 2 showed that only 9 percent of voters were considering him—although those who had heard about him recently had a 64 percent favorable impression, and 61 percent said they would definitely support him.

But few have heard of him because interest groups that usually support the Democratic Party, especially labor unions, have almost entirely embraced McGinty, the establishment favorite. Perhaps it shouldn’t be surprising that an outsider candidate hasn’t picked up any labor endorsements, but then neither has Sestak, who may have thoroughly alienated much of the Democratic Party elite over the last six years but has a strong record of support for the Affordable Care Act and the Employee Free Choice Act in Congress.

A similar dynamic is occurring in the presidential election, where younger and more progressive Democratic voters have transformed the long-shot candidacy of socialist Bernie Sanders into a genuine competitor to Hilary Clinton. (Fetterman is also one of the only candidates in Pennsylvania to endorse Sanders.) Yet despite the Vermont senator’s long history of voting ideologically in lockstep with the AFL-CIO and most other major unions, almost all of the prominent labor organizations have endorsed Clinton. And that very much includes SEIU, which is the principal force backing a $15 federal minimum wage—which Clinton does not support.

“There is a kind of institutional conservatism even among liberal unions,” says Nelson Lichtenstein, a professor of history at the University of California, Santa Barbara, and author of Achieving Workers’ Rights in the Global Economy. “Labor feels that it’s permanently on the defensive, and they don’t want to take a chance. If that’s the case, then they just go with the status quo and go with whatever Democrat [the party supports]. It’s not imaginative, it’s not mobilizing the base, it’s not daring. But there’s a kind of logic to it.”

In this year of progressive insurgency and backlash against the status quo, progressive activists and Sanders-inspired voters may be wondering why organized labor seems so resolutely set on backing Democratic candidates with less-expansive and less-left-wing visions for the future of the party and the nation. Indeed, many union staffers voice substantial support off the record for candidates like Fetterman and Sanders, who push the leftward envelope of what is possible within the Democratic Party. Rank-and-file party members and activists at political events in the western Pennsylvania steel towns of Sharon and Butler, or in the longstanding African American ghettos of North Philadelphia, tend to back Fetterman or Sestak. But that isn’t reflected in endorsements from Democratic politicians or in the interest groups that support the party, particularly labor.

That shouldn’t be surprising. After World War II, the closest the labor movement ever came to forging an alternative political path was during the 1948 election, when Walter Reuther and the powerful United Auto Workers (UAW) prepared for the supposedly inevitable defeat of Harry Truman. Few of the postwar labor leaders were enamored of the unelected incumbent, and they sought an escape from a Democratic Party limited in the breadth of its reform schemes by reactionary Dixiecrats. Reuther denounced “both the Republican and Democratic parties as presently constituted” and made plans for the formation of a labor party. But then union voters secured Truman’s surprise victory, along with a Democratic takeover of Congress, and such talk died down. The unions had already seen what had happened when they lost state support in 1947, when the Republican Congress passed the repressive Taft-Hartley Act. To them, it seemed better to remain in the camp of the party that once again held all the power.

Since then there has been a long history of small-“c” conservatism in the U.S. labor movement when it comes to political endorsements. This is especially true of larger unions that have more access to powerful politicians and that depend on their backing for the transactional deals that secure collective-bargaining rights or less adversarial negotiations. That usually means supporting incumbents over those who may be ideologically aligned with labor’s actual interests.

Even the most militant unions will engage in this kind of realpolitik. In 2002, the large and progressive SEIU 1199 endorsed Republican governor George Pataki in his bid for a third term after he approved wage increases. In 1997, the influential Los Angeles County Federation of Labor endorsed Republican incumbent Richard Riordan in the Los Angeles mayoral election against left-wing icon Tom Hayden, who wasn’t expected to win (and didn’t). “It was a vote for practicality,” one anonymous union leader explained. “We read the polls, too.”

“An endorsement is a kind of a bet, and unions tend to bet on the favorite, not on a longshot,” says Richard Yeselson, a veteran of the labor movement and contributing editor at Dissent magazine. “They are cautious and careful even when their tactics are militant. It’s not like May ’68 in France, they don’t want to take over the government.” He adds that “the more powerful the union,” the more likely it is to endorse an establishment candidate, “because they have more access and more influence.”

As progressive challengers have become increasingly common in recent years, these dynamics have dogged left-wing insurgencies across the country. In 2014, the Working Families Party endorsed Andrew Cuomo, who is in many ways the embodiment of a labor-unfriendly centrist Democrat. SEIU 32BJ supported Christine Quinn in the 2013 New York Democratic mayoral primary, despite the candidate’s reputation as the successor to Michael Bloomberg.

But in recent years, some labor unions have become increasingly likely to break from the Democratic establishment when the incumbent is seen as especially noxious, as in labor’s recent attempt to unseat Chicago Mayor Rahm Emanuel. (But even then, Unite Here decided to support the mayor, arguing in effect that its organizers read the polls, too.) The Working Families Party surprised many by endorsing Bernie Sanders in the 2016 election, as did more militant and smaller unions like the National Nurses United, the International Longshoremen and Warehouse Union, and the United Electrical Workers.

If there are increasing exceptions to the conservatism of labor’s endorsements, they seem to only come if there is either a powerful disincentive to back a candidate (like Emanuel) or a very good case for backing a strong progressive option (like New York City Mayor Bill de Blasio). In the Pennsylvania Senate race, McGinty may not be a favorite of party activists, who distrust her record with the Clintons and her measured embrace of the fracking industry, but she’s proved adaptable. In her 2014 gubernatorial campaign, she supported a $9 minimum wage, but this year she announced her support for a $15 wage threshold and won the endorsement of the SEIU, which is backing the wage hike.

“The other two candidates are good people but neither one has the record of being a champion and achieving the kind of concrete results that Katie does,” says Neal Bisno, president of SEIU Healthcare PA. “Katie McGinty is a proven progressive champion who is committed to tackling income inequality, lifting wages, and promoting worker organization—much more so than either of the other two candidates.”

Fetterman may have supported a $15 minimum wage earlier than his two opponents, and Sestak may have a sterling liberal record in the House, but McGinty has proved herself a progressive team player only recently. In addition to announcing her change of heart on the $15 wage minimum, Bisno says that McGinty was instrumental in Governor Tom Wolf’s efforts to give Pennsylvania home-care workers unionization rights.

In a race where anywhere from one-fifth to half of the voters remain undecided, television advertisements and get-out-the-vote efforts—funded by groups like SEIU Healthcare PA—will prove decisive. Without the support of any interest groups, and with little chance to build a base of small donors in a presidential election year, Fetterman’s campaign has floundered, and even the amply funded Sestak is now playing catchup to McGinty in campaign contributions.

Six months after her impassioned and impromptu speech for Fetterman, Elizabeth Arnold is now working as an organizer for Bernie Sanders’s campaign in Pennsylvania. She still speaks passionately in favor of Fetterman, even though his campaign hasn’t gained momentum. As for labor’s lack of support—well, that’s to be expected. Few of Pennsylvania’s unions have endorsed Sanders either.

Arnold, for one, is not surprised. Endorsements, she writes to the Prospect, “are decided in D.C. and get handed down.” She argues that “rank-and-file” Democrats don’t know much about any of the Senate candidates, but that many would no doubt like Fetterman for his integrity and honesty—an assertion that is supported by the latest polling. But at this point, without labor support or the funding it entails, it is unlikely that enough voters will discover him before Tuesday.